This application is based on Japanese Patent Application Nos. 2000-334177 filed Nov. 1, 2000, and 2001-049880 filed Feb. 26, 2001, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a novel method of designing an ophthalmic lens, and an ophthalmic lens produced by the method. More particularly, the present invention is concerned with a method of determining specifications of the ophthalmic lens, which ophthalmic lens assures a high degree of visual acuity with high stability while avoiding a variation of the visual acuity even when the optical axis of the ophthalmic lens is offset from the optical axis of the eye of the lens wearer due to a movement of the lens on the cornea or in the eye. Further, the present invention is concerned with a method of producing the ophthalmic lens based on the determined specifications. The present invention also relates to an ophthalmic lens which is produced by the method.
2. Discussion of Related Art
Conventionally, an ophthalmic lens such as a contact lens and an intraocular lens is designed independently of the eye to which the ophthalmic lens is applied. In other words, the ophthalmic lens is produced so as to assure an optimum characteristic of imaging on its optical axis. For attaining the optimum imaging characteristic, various techniques are proposed. For instance, Japanese Patent No. 2859092 discloses a method of designing an ophthalmic lens, wherein a path of light which is incident on each reference point on one of the opposite lens surfaces that has been already formed into an intended configuration is taken into account, and an angle of inclination of the other lens surface at a point located on the light path is determined so that the light undergoes an intended refracting force. Japanese Patent No. 2913191 discloses a method of designing a lens by a ray tracing technique in an attempt to reduce a spherical aberration of the lens. In the disclosed method, the configuration of the refracting surface of the lens is designed as follows. The inclination of a curved surface at an arbitrary height as measured from the optical axis of the refracting surface is determined such that the light passing the arbitrary height passes a desired final pass point which is set in advance, after the light has passed through the lens. Based on the successively obtained inclinations of the curved surface at different heights, the configuration of the curved surface as a whole is designed.
Japanese Patent No. 3022640 discloses a method of producing an aspheric lens, comprising the steps of: constructing a mathematical model of a system of a human eye and a preliminary lens; performing an analysis using the model to trace light ray paths through the lens-eye system; varying a value of the aspheric constant k for the preliminary lens to achieve a lens-eye system with a trace of light ray paths optimized for sharpest focus by minimizing retinal spot size of the rays.
The above-described conventional methods of designing or producing the ophthalmic lens aim at optimizing the imaging characteristic on the optical axis of the lens. These methods are for optimizing the imaging characteristic with respect to an optical schematic of the human eye (schematic eye) by taking into account the eye optical system. The ophthalmic lens designed or produced according to the conventional methods assures the optimum imaging characteristic on its optical axis. These methods, however, ignore the fact that the center of the pupil of the eye (the optical axis of the eye) is usually not aligned with the optical center of the lens while the lens is applied to or worn on the eye. Accordingly, the optical characteristic of the optical system consisting of the lens and the eye tends to be deteriorated when the lens is offset from the optical axis of the eye. For example, the optical center of the contact lens is not aligned with the center of the pupil of the eye in most instances when the contact lens is worn on the eye. The movement of the contact lens on the cornea of the lens wearer""s eye and the stable position of the contact lens on the cornea in which the contact lens is stably held in place vary depending upon the individual lens wearers. Accordingly, the visual acuity and stability tend to fluctuate depending upon the movement and stable position of the contact lens on the cornea of the eye.
The present invention was developed in the light of the background art described above. It is therefore a first object of the invention to provide a method of designing an ophthalmic lens which exhibits optical characteristics equal to or close to those exhibited by the ophthalmic lens when its optical axis is aligned with the optical axis of the eye on which the ophthalmic lens is worn, or in which the ophthalmic lens is inserted, even if the optical axis of the ophthalmic lens is displaced or offset from that of the eye.
It is a second object of the invention to provide a method of producing an intended ophthalmic lens by the designing method described above.
It is a third object of the invention to provide an ophthalmic lens produced by the designing method described above.
The first object indicated above may be achieved according to a first aspect of the present invention, which provides a method of designing an ophthalmic lens, comprising the steps of: determining specifications of a temporary lens such that said temporary lens gives an optical power required by a wearer of the ophthalmic lens; applying said temporary lens to a prescribed schematic eye, and effecting emmetropization of an optical system consisting of said temporary lens and said schematic eye; obtaining an optical characteristic of said optical system at a position of an optical axis of said temporary lens which is offset from an optical axis of said schematic eye by a predetermined offset amount; obtaining successively optical characteristics corresponding to different configurations of said temporary lens with said axes of said temporary lens and said schematic eye being offset from each other by said predetermined offset amount; selecting optimum one of said different configurations of said temporary lens which gives optimum one of the successively obtained optical characteristics; and determining specifications of an intended ophthalmic lens as a final product, based on the selected optimum configuration of said temporary lens.
In the present method described above, the optical characteristic of the optical system consisting of the schematic eye and the temporary lens is obtained with the temporary lens being applied to the schematic eye. Further, the optical characteristic of the optical system is obtained at the position of the optical axis of the temporary lens which is offset from the optical axis of the schematic eye by the predetermined offset amount that is expected when the ophthalmic lens is actually applied to the eye of the lens wearer. The optical characteristics of the optical system are successively obtained corresponding to different configurations of the temporary lens, and the optimum one of the different configurations of the temporary lens which gives the optimum one of the successively obtained optical characteristics is selected. On the basis of the selected configuration of the temporary lens, the specifications of the intended ophthalmic lens are determined. Accordingly, the ophthalmic lens whose specifications are determined based on the optimum configuration of the temporary lens which gives the optimum optical characteristic assures an excellent optical characteristic even if the optical axis of the ophthalmic lens is offset from that of the lens wearer""s eye while the ophthalmic lens is actually applied to the eye. Therefore, the visual acuity and stability can be effectively enhanced.
The above-indicated first object of the present invention may also be achieved according to a second aspect of the invention, which provides a method of designing an ophthalmic lens, comprising the steps of: determining specifications of a temporary lens such that the temporary lens gives an optical power required by a wearer of the ophthalmic lens; applying the temporary lens to a prescribed schematic eye, and effecting emmetropization of an optical system consisting of the temporary lens and the schematic eye; obtaining, as a reference characteristic, an optical characteristic of the optical system at a position of an optical axis of the temporary lens which is aligned with an optical axis of the schematic eye; obtaining, as a variable characteristic, an optical characteristic of the optical system at a position of the optical axis of the temporary lens which is offset by a predetermined offset amount from the optical axis of the schematic eye; obtaining successively the reference characteristics and the variable characteristics corresponding to different configurations of the temporary lens; selecting one of the different configurations of the temporary lens, which gives a minimum difference between the reference characteristic and the variable characteristic; and determining specifications of an intended ophthalmic lens as a final product, based on the selected configuration of the temporary lens.
In the present method described above, the optical characteristic of the optical system consisting of the schematic eye and the temporary lens which is applied thereto is obtained as the reference characteristic when the emmetropization of the optical system is established. Further, the optical characteristic of the optical system is obtained as the variable characteristic when the optical axis of the temporary lens is offset by the predetermined offset amount from the optical axis of the schematic eye. The reference characteristics and variable characteristics are successively obtained corresponding to different configurations of the temporary lens. From among the different configurations of the temporary lens, one of the configurations of the temporary lens which gives a minimum difference between the reference and variable characteristics is selected. On the basis of the selected configuration of the temporary lens which gives the minimum difference between the reference and variable characteristics, the specifications of the intended ophthalmic lens are determined. Therefore, the ophthalmic lens designed according to the present method described above assures an improved optical characteristic even when the optical axis of the lens is offset from that of the eye to which the ophthalmic lens is applied.
The above-indicated first object of the invention may also be attained according to a third aspect of the invention, which provides a method of designing an ophthalmic lens, comprising the steps of: determining specifications of a temporary lens such that the temporary lens gives an optical power required by a wearer of the ophthalmic lens; applying the temporary lens to a prescribed schematic eye such that the temporary lens is located at a position on the schematic eye corresponding to a stable position on an eye of the wearer in which the ophthalmic lens is held in place; obtaining an optical characteristic of an optical system consisting of the temporary lens and the schematic eye with the temporary lens being located at the stable position on the schematic eye, obtaining successively optical characteristics corresponding to different configurations of the temporary lens; selecting optimum one of the different configurations of the temporary lens which gives optimum one of the successively obtained optical characteristics; and determining specifications of an intended ophthalmic lens as a final product, based on the selected optimum configuration of the temporary lens.
In the present method described above, the optical characteristic of the optical system consisting of the temporary lens and the schematic eye is obtained with the temporary lens being located at the stable position on the schematic eye corresponding to the stable position on the lens wearer""s eye in which the ophthalmic lens is held in place. In other words, the optical characteristic of the optical system is obtained at a position of the optical axis of the temporary lens which is offset from the optical axis of the schematic eye by the predetermined offset amount that is expected when the ophthalmic lens is actually applied to the lens wearer""s eye. The optical characteristics of the optical system are successively obtained corresponding to different configurations of the temporary lens. In the present method, the optimum one of the different configurations of the temporary lens which gives the optimum one of the successively obtained optical characteristic is selected, and the specifications of the intended ophthalmic lens are determined on the basis of the selected optimum configuration of the temporary lens which gives the optimum optical characteristic. Accordingly, the ophthalmic lens whose specifications are determined based on the optimum configuration of the temporary lens which gives the optimum optical characteristic assures an excellent optical characteristic even if the optical axis of the ophthalmic lens is offset from that of the wearer""s eye while the ophthalmic lens is actually applied to the eye. Therefore, the visual acuity and stability can be effectively enhanced.
The above-indicated first object of the invention may also be attained according to a fourth aspect of the invention, which provides a method of designing an ophthalmic lens, comprising the steps of: determining specifications of a temporary lens such that the temporary lens gives an optical power required by a wearer of the ophthalmic lens; applying the temporary lens to a prescribed schematic eye such that the temporary lens is located at a position on the schematic eye corresponding to a stable position on an eye of the wearer in which the ophthalmic lens is held in place, and effecting emmetropization of the optical system with the temporary lens being located at the stable position on the schematic eye; obtaining an optical characteristic of the optical system while the emmetropization of the optical system is established, obtaining successively optical characteristics corresponding to different configurations of the temporary lens; selecting optimum one of the different configurations of the temporary lens which gives optimum one of the successively obtained optical characteristics; and determining specifications of an intended ophthalmic lens as a final product, based on the selected optimum configuration of the temporary lens.
In the present method described above, the temporary lens is located at the stable position on the schematic eye corresponding to the stable position on the lens wearer""s eye in which the ophthalmic lens is held in place. The optical characteristic of the optical system consisting of the schematic eye and the temporary lens which is located at the stable position on the schematic eye is obtained while the emmetropization of the optical system is established. The optical characteristics are successively obtained corresponding to the different configurations of the temporary lens while the emmetropization of the optical system is established. In the present method, the optimum one of the different configurations of the temporary lens which gives the optimum one of the successively obtained optical characteristics is selected, and the specifications of the intended ophthalmic lens are determined on the basis of the selected optimum configuration of the temporary lens which gives the optimum optical characteristic. Accordingly, the present method permits an easy and advantageous designing of the ophthalmic lens which exhibits an excellent optical characteristic.
In one preferred form of the above-described first and second aspects of the invention, the emmetropization of the optical system is effected with the optical axes of the temporary lens and the schematic eye being aligned with each other.
In one preferred form of the above-described first, second and fourth aspects of the invention, the emmetropization of the optical system is effected by changing at least one of the following parameters selected from the group consisting of: an axial length of the schematic eye, a radius of curvature of a front surface of a cornea of the schematic eye, a radius curvature of a back surface of the cornea of the schematic eye, a radius of curvature of a front surface of a crystalline lens of the schematic eye, a radius of curvature of a back surface of the crystalline lens of the schematic eye, a diameter of a pupil of the schematic eye, and an optical power of a corrective lens.
In the above-described methods according to the first through fourth aspects of the invention, the optical characteristics of the optical system is preferably calculated by at least one of a wavefront aberration, a point spread function (PSF), a modulation transfer function (MTF), and a resolving power, for thereby facilitating a mathematical analysis of the optical characteristic of the optical system.
In another preferred form of the above-indicated first through fourth aspects of the invention, the schematic eye corresponds to an eye of the wearer who wears the ophthalmic lens.
In yet another preferred form the above-indicated first and second aspects of the invention, the ophthalmic lens is a contact lens, and the predetermined offset amount of the optical axis of the temporary lens from the optical axis of the schematic eye is not greater than 30xc2x0. The predetermined offset amount is preferably divided into a plurality of divisions, each division being not greater than 10xc2x0, and the optical characteristic is obtained at an end point of each of the plurality of divisions. According to this arrangement, the optimum optical characteristic is advantageously selected by taking into account the optical characteristics obtained at the respective end points of the plurality of divisions of the offset amount.
In a further preferred form the above-indicated first and second aspects of the invention, the ophthalmic lens is an intraocular lens, and the predetermined offset amount of the optical axis of the temporary lens from the optical axis of the schematic eye is not greater than 4 mm. The predetermined offset amount is preferably divided into a plurality of divisions, each division being not greater than 2 mm, and the optical characteristic is obtained at an end point of each of the plurality of divisions. According to this arrangement, the optimum optical characteristic is advantageously selected by taking into account the optical characteristics obtained at the respective end points of the plurality of divisions.
The above-described second object of the invention may be attained according to a fifth aspect of the invention, which provides a method of producing an ophthalmic lens based on the specifications determined by any one of the methods according to the first through fourth aspects of the invention described above. The ophthalmic lens produced by the present method exhibits an excellent optical characteristic.
The above-indicated third object of the invention may be attained according to a sixth aspect of the invention, which provides an ophthalmic lens produced by any one of the methods according to the first through fourth aspects of the invention described above. The present ophthalmic lens assures improved visual acuity and stability even if the optical axis of the ophthalmic lens is offset from the optical axis of the eye of the lens wearer.